1. Field of the Invention
The present invention relates to a low-loss microwave dielectric material suited for use in a circuit processing electric signals of microwaves, for example, in an SHF band, and to a process for preparing the same.
2. Prior Art of the Invention
A low-loss dielectric material is used for a dielectric resonator in an SHF band circuit. More specifically, the dielectric resonator is coupled with a filter, a Gunn oscillator or an FET oscillator. Thus, it is an indispensable element for stabilizing frequency. The dielectric resonator is used in a receiver for broadcasting via a broadcasting satellite or SHF broadcasting on ground. For improving the performance of the receiver, there has been a serious demand for an improvement in Q factor of the dielectric resonator. For the purpose, the dielectric material of the resonator is required to have a relative dielectric constant of 25 to 40, an unloaded Q factor of 10.sup.4 or more and a temperature coefficient of resonant frequency of within .+-.10 ppm/.degree.C. in a 10 GHz band and at about room temperature.
Examples of conventional dielectric materials practically used as a resonator satisfying the above-mentioned requirements include ceramics of, for example, Ba.sub.2 Ti.sub.9 O.sub.20, and ceramics of (Zn.sub.0.8 Sn.sub.0.2)TiO.sub.4. These materials satisfy the above-mentioned conditions as regards relative dielectric constant and the temperature coefficient of resonant frequency but not unloaded Q factor. The unloaded Q factors of the Ba.sub.2 Ti.sub.9 O.sub.20 and (Zn.sub.0.8 Sn.sub.0.2)TiO.sub.4 ceramics with the addition of 0.5-2.0 mol % Mn are about 5000 in 7-10 GHz band (see "Effect of Mn Doping on Ceramics with a Low Loss and a High Dielectric Constant in X band" by Shoichiro Nomura et al., Japanese Applied Physics Association-Conference Paper 2a-I-4 (p. 763), April, 1982). Thus, no material has been found that satisfies all the above-mentioned three conditions.
In this age expecting practical broadcasting via a broadcasting satellite in the near future, there has been an ever-increasing necessity for a dielectric material meeting all the above-mentioned conditions.